Denos C. Gazis

SCHOOL BUS ROUTING BY COMPUTER

A PROCEDURE IS DESCRIBED FOR THE DESIGNING OF SCHOOL BUS ROUTES BY COMPUTER. THE PROCEDURE IS MORE FLEXIBLE THAN PREVIOUSLY PUBLISHED ONES IN A NUMBER OF WAYS. THE OBJECTIVE FUNCTION INCLUDES THE REDUCTION OF STUDENT TRAVEL TIME, U-TURNS, AND BUS OVERLOADING, AS WELL AS THE REDUCTION OF BUS TRAVEL TIME. THE PROCEDURE CAN ALSO HANDLE ONE-WAY STREETS, A BUS GARAGE OTHER THAN AT THE SCHOOL SITE AND THE REQUIREMENT THAT AT CERTAIN STOPS THE BUS MUST PICK UP CHILDREN FROM ONE PARTICULAR SIDE OF THE ROAD. THE PROCEDURE IS AN EXTENSION OF THE CLARKE AND WRIGHT ALGORITHM FOR SCHEDULING DELIVERY VEHICLES. /TRRL/

Modeling and optimal control of congested transportation systems

An approach is discussed for the modeling of congested transportation systems as store-and-forward networks analogous to communication networks of this type but with a finite travel time between nodes. A variety of approaches is suggested, and illustrated by examples, for the allocation of the usage of the arcs of the network by various competing units of traffic.

Traffic control: From hand signals to computers'

An overview is given of current applications of computers to traffic control. It includes a discussion of types of hardware and control strategies used in computerized systems developed for the control of urban street networks, as well as critical traffic links such as freeways and tunnels. Some remarks are made concerning possible future development in the use of computers for better management of traffic facilities.

Traffic flow theory

The traffic theorist of today has an ever-increasing capacity to bring a wide range of technical skills to bear on the pressing problems of traffic congestion, delays, and accidents with their ensuing economic and personal costs. These problems are very complex, but well-defined aspects of them can be dealt with theoretically in explicit mathematical form. Illustrations are given as to how this may be done in meaningful ways to find the relationships between important variables and to determine the influence of parameter values on the performance of traffic systems. The problems discussed consider traffic flow in single and multiple lanes, interference between vehicles and queue formations, single and multiple intersection flows and control and road networks.

A communication network architecture for transportation information systems

An emerging application of mobile computing and communication is the delivery of information related to the transportation system to drivers and travelers. Such real-time information would be very valuable in providing services such as pre-trip planning, route guidance, intermodal transportation, yellow pages, and ride matching and reservation. This so-called advanced traveler information system (ATIS) is an important subset of an intelligent transportation system (ITS). The authors are developing an ATIS operational field test called SWIFT (Seattle wide-area information for travelers) in the Seattle metropolitan area which uses technological advances in wireless communication, personal digital assistants (PDA), and traffic modeling and analysis. SWIFT uses an advanced 19 kbps FM subcarrier broadcast medium for the delivery of transportation information as well as personal paging information. Preliminary description of the logical and physical architecture of the SWIFT system along with communication loading analysis for this system, are presented.

Traffic Control, Time—Space Diagrams, and Networks

The object of traffic control is largely to minimize the delay, or travel time, of the users of a traffic system. Both the aggregate delay to all the users of a traffic system and the maximum individual delay are to be considered. Other objectives of traffic control are the decrease of the number of stops, increase of smoothness of driving, and increase of safety.

Resource allocation in a large decentralized enterprise

Abstract We present a model of an enterprise comprising several operating units pursuing their production goals with a fair degree of autonomy, but under resource constraints imposed by a headquarters function. Specifically, each operating unit is assumed to seek a maximization of a perceived market value of its product output, subject to constraints on resources such as capital for plants and equipment, headcount, etc. imposed by headquarters. The headquarters function pursues a global optimization problem which takes into account the market values of all the products of the operating units, but also the cost of the resources and their regulation. Under suitable assumptions of linearity, the operation of the enterprise is formulated as a novel hierarchical structure of linear programming problems. An algorithm is presented for the solution of a class of such problems.

Lattice vibrational waves in cubic crystal plates

SummaryAn investigation is given of the lowest symmetric (extensional) and the lowest antisymmetric (flexural) mode of waves in a cubic crystal plate bounded by two planes of symmetry. The investigation was carried out using the continuum theory of anisotropic elasticity, and also using a simple cubic lattice model. Particular attention was given to the change of the character of both the extensional and flexural mode, which takes place as the wave length is decreased from infinity down to values of the order of the plate thickness. Both modes tend to become surface modes whenever surface waves are possible along the direction of propagation. However, some essential differences were observed, regarding this transition from bulk modes to surface modes, between materials which propagateRayleigh surface waves and those which propagate generalizedRayleigh surface waves.ZusammenfassungEs werden die niedrigsten Schwingungsformen in einem kubischen Plattenkristall, der von zwei Symmetrieebenen begrenzt wird, untersucht, und zwar sowohl die symmetrische (Dehnungs-) als auch die antisymmetrische (Biegungs-) Schwingung. Die Untersuchung wird mit Hilfe der Kontinuumstheorie anisotroper elastischer Medien sowie unter Verwendung des Modells eines einfachen kubischen Gitters durchgeführt. Besondere Aufmerksamkeit wird der Änderung des Charakters der Dehnungs- und der Biegeschwingung gewidmet, welche bei Verkleinerung der Wellenlänge von sehr großen Werten auf solche von der Größenordnung der Plattendicke auftritt. Beide Wellenarten haben das Bestreben, Oberflächenwellen zu werden, solange das Auftreten von Oberflächenwelles in der Ausbreitungsrichtung möglich ist. Es werden aber einige wesentliche Unterschiede beim Übergang von Körperwellen zu Oberflächenwellen beobachtet, je nachdem, ob es sich um Stoffe handelt, in denenRayleighsche Oberflächenwellen oder solche, in denen verallgemeinerteRayleighsche Oberflächenwellen entstehen.

CONGESTION ABATEMENT IN ITS THROUGH CENTRALIZED ROUTE ALLOCATION

We present a methodology for congestion abatement in ITS. It is based on the centralized management of route allocation to individual vehicles, aimed at minimizing the contention for the use of roadway facilities and the resulting congestion. The underlying principle is that of treating a system as a Store-and-Forward system, in which the use of roadways is allocated to individual traffic units in a way that minimizes the overall delay to the users of the system. Individual vehicles are given the opportunity to use Service Channels assigned by a Traffic Management Center (TMC). The Service Channels provide the best routes to individual travelers consistent with the goal of global system optimization. A discussion is given of the possible evolution from early deployment of ITS when only a few vehicles Will be equipped with ITS instrumentation, to the days of full IVHS deployment.

Equivoluminal, lamé-type waves in composite hollow cylinders

Abstract A description is given of axially symmetric, equivoluminal waves propagating along the axis of a composite cylinder made up of concentric hollow cylinders. The waves can be viewed as a superposition of SV-type waves reflected at the free boundaries, and involve motion in planes through the cylinder axis. Waves of this type can exist only if the shear wave velocity is the same in the various media of the composite cylinder and, in addition, the thicknesses of the different media are proportional to the zeros of a simple transcendental equation.